This invention relates to a spray dampening system of a type used for spraying dampening fluid onto the dampening roller or inking roller of an offset printing press, and more particularly the invention relates to a spray dampening system in which the width of the spray pattern may be adjusted while maintaining a uniform delivery of dampening fluid across the width of the dampening roller or inking roller.
In a spray dampening system, the dampening fluid is sprayed onto the press rollers by means of a linear array of spray nozzles with the spray patterns of the individual nozzles merging to form a continuous composite spray pattern across the surface of the press roller. It is important in obtaining proper dampening that the distribution of dampening fluid be as uniform as possible. There should be no starved areas where the amount of dampening fluid is substantially less than the other areas on the surface of the roller, and the overlapping of the adjacent individual spray patterns should be minimized so that there is little or no excessive dampening fluid applied to any portion of the dampening roller.
Various attempts have been made at adjusting the amount of dampening fluid applied to the dampening roll. In U.S. Pat. No. 4,064,801, the valves of the dampening system fluctuate between open and closed positions to regulate the amount of dampening fluid applied to the rolls, and in U.S. Pat. No. 4,649,818, the nozzles are pulsed on and off with the pulse width being adjusted, thereby providing a very precise control over the amount of dampening fluid delivered. In U.S. Pat. No. 4,815,375, there is a delivery of dampening fluid through alternate laterally adjacent nozzles. In U.S. Pat. No. 4,198,907, several independently adjustable needle valves are turned on and off at the same time to control the page dampening, and with proper valving, such as the valves disclosed in U.S. Pat. No. 4,394,873, the nozzle valves can be shut off, or the amount of spray emanating from the nozzle may be regulated. None of the prior art systems, however, allow an adjustment to be made in the width of the dampening pattern, except by shutting off the end nozzles in the nozzle array. However, shutting off the end nozzles only permits an adjustment from a full width pattern to a pattern which is less than a full width by one or two spray nozzle pattern widths. Such systems would not permit an adjustment from say, 60 inches to 50 inches in width.
It of course is possible to move the nozzles toward each other and away from each other in order to narrow the width of the composite spray pattern. However, this would not be satisfactory because as the nozzles are moved toward each other there would be an overlap of the adjacent nozzle spray patterns resulting in overwetting of portions of the dampening roller.
The present invention permits the width of the composite spray pattern to be adjusted to the precise width desired while preventing excessive overlapping of the laterally adjacent individual spray patterns. The result is a system which delivers a uniform composite pattern of spray dampening fluid over a very precise width of the dampening roller.